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Tools/Linux64/hdf5/share/hdf5_examples/c/h5_extlink.c

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/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* Copyright by The HDF Group. *
* All rights reserved. *
* *
* This file is part of HDF5. The full HDF5 copyright notice, including *
* terms governing use, modification, and redistribution, is contained in *
* the COPYING file, which can be found at the root of the source code *
* distribution tree, or in https://www.hdfgroup.org/licenses. *
* If you do not have access to either file, you may request a copy from *
* help@hdfgroup.org. *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
/* This program demonstrates how to create and use "external links" in
* HDF5.
*
* External links point from one HDF5 file to an object (Group, Dataset, or
* committed Datatype) in another file.
*/
#include "hdf5.h"
#include <string.h>
#define SOURCE_FILE "extlink_source.h5"
#define TARGET_FILE "extlink_target.h5"
#define PREFIX_SOURCE_FILE "extlink_prefix_source.h5"
#define SOFT_LINK_FILE "soft_link.h5"
#define SOFT_LINK_NAME "soft_link_to_group"
#define UD_SOFT_LINK_NAME "ud_soft_link"
#define TARGET_GROUP "target_group"
#define UD_SOFT_CLASS 65
#define HARD_LINK_FILE "hard_link.h5"
#define HARD_LINK_NAME "hard_link_to_group"
#define UD_HARD_LINK_NAME "ud_hard_link"
#define UD_HARD_CLASS 66
#define PLIST_LINK_PROP "plist_link_prop"
#define UD_PLIST_CLASS 66
/* Basic external link example
*
* Creates two files and uses an external link to access an object in the
* second file from the first file.
*/
static void
extlink_example(void)
{
hid_t source_file_id, targ_file_id;
hid_t group_id, group2_id;
/* Create two files, a source and a target */
source_file_id = H5Fcreate(SOURCE_FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);
targ_file_id = H5Fcreate(TARGET_FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);
/* Create a group in the target file for the external link to point to. */
group_id = H5Gcreate2(targ_file_id, "target_group", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
/* Close the group and the target file */
H5Gclose(group_id);
/* Create an external link in the source file pointing to the target group.
* We could instead have created the external link first, then created the
* group it points to; the order doesn't matter.
*/
H5Lcreate_external(TARGET_FILE, "target_group", source_file_id, "ext_link", H5P_DEFAULT, H5P_DEFAULT);
/* Now we can use the external link to create a new group inside the
* target group (even though the target file is closed!). The external
* link works just like a soft link.
*/
group_id = H5Gcreate2(source_file_id, "ext_link/new_group", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
/* The group is inside the target file and we can access it normally.
* Here, group_id and group2_id point to the same group inside the
* target file.
*/
group2_id = H5Gopen2(targ_file_id, "target_group/new_group", H5P_DEFAULT);
/* Don't forget to close the IDs we opened. */
H5Gclose(group2_id);
H5Gclose(group_id);
H5Fclose(targ_file_id);
H5Fclose(source_file_id);
/* The link from the source file to the target file will work as long as
* the target file can be found. If the target file is moved, renamed,
* or deleted in the filesystem, HDF5 won't be able to find it and the
* external link will "dangle."
*/
}
/* External link prefix example
*
* Uses a group access property list to set a "prefix" for the filenames
* accessed through an external link.
*
* Group access property lists inherit from link access property lists;
* the external link prefix property is actually a property of LAPLs.
*
* This example requires a "red" directory and a "blue" directory to exist
* where it is run (so to run this example on Unix, first mkdir red and mkdir
* blue).
*/
static void
extlink_prefix_example(void)
{
hid_t source_file_id, red_file_id, blue_file_id;
hid_t group_id, group2_id;
hid_t gapl_id;
/* Create three files, a source and two targets. The targets will have
* the same name, but one will be located in the red directory and one will
* be located in the blue directory */
source_file_id = H5Fcreate(PREFIX_SOURCE_FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);
red_file_id = H5Fcreate("red/prefix_target.h5", H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);
blue_file_id = H5Fcreate("blue/prefix_target.h5", H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);
/* This test needs a red and a blue directory in the filesystem. If they're not present,
* trying to create the files above will fail.
*/
if (red_file_id < 0 || blue_file_id < 0)
printf("This test requires directories named 'red' and 'blue' to exist. Did you forget to create "
"them?\n");
/* Create an external link in the source file pointing to the root group of
* a file named prefix_target.h5. This file doesn't exist in the current
* directory, but the files in the red and blue directories both have this
* name.
*/
H5Lcreate_external("prefix_target.h5", "/", source_file_id, "ext_link", H5P_DEFAULT, H5P_DEFAULT);
/* If we tried to traverse the external link now, we would fail (since the
* file it points to doesn't exist). Instead, we'll create a group access
* property list that will provide a prefix path to the external link.
* Group access property lists inherit the properties of link access
* property lists.
*/
gapl_id = H5Pcreate(H5P_GROUP_ACCESS);
H5Pset_elink_prefix(gapl_id, "red/");
/* Now if we traverse the external link, HDF5 will look for an external
* file named red/prefix_target.h5, which exists.
* To pass the group access property list, we need to use H5Gopen2.
*/
group_id = H5Gopen2(source_file_id, "ext_link", gapl_id);
/* Now we can use the open group ID to create a new group inside the
* "red" file.
*/
group2_id = H5Gcreate2(group_id, "pink", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
/* Close both groups. */
H5Gclose(group2_id);
H5Gclose(group_id);
/* If we change the prefix, the same external link can find a file in the blue
* directory.
*/
H5Pset_elink_prefix(gapl_id, "blue/");
group_id = H5Gopen2(source_file_id, "ext_link", gapl_id);
group2_id = H5Gcreate2(group_id, "sky blue", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
/* Close both groups. */
H5Gclose(group2_id);
H5Gclose(group_id);
/* Each file has had a group created inside it using the same external link. */
group_id = H5Gopen2(red_file_id, "pink", H5P_DEFAULT);
group2_id = H5Gopen2(blue_file_id, "sky blue", H5P_DEFAULT);
/* Clean up our open IDs */
H5Gclose(group2_id);
H5Gclose(group_id);
H5Pclose(gapl_id);
H5Fclose(blue_file_id);
H5Fclose(red_file_id);
H5Fclose(source_file_id);
/* User-defined links can expand on the ability to pass in parameters
* using an access property list; for instance, a user-defined link
* might function like an external link but allow the full filename to be
* passed in through the access property list.
*/
}
/* Soft Link example
*
* Create a new class of user-defined links that behave like HDF5's built-in
* soft links.
*
* This isn't very useful by itself (HDF5's soft links already do the same
* thing), but it can serve as an example for how to reference objects by
* name.
*/
/* We need to define the callback function that the soft link will use.
* It is defined after the example below.
* To keep the example simple, these links don't have a query callback.
* In general, link classes should always be query-able.
* We might also have wanted to supply a creation callback that checks
* that a path was supplied in the udata.
*/
static hid_t UD_soft_traverse(const char *link_name, hid_t cur_group, const void *udata, size_t udata_size,
hid_t lapl_id, hid_t dxpl_id);
static void
soft_link_example(void)
{
hid_t file_id;
hid_t group_id;
/* Define the link class that we'll use to register "user-defined soft
* links" using the callbacks we defined above.
* A link class can have NULL for any callback except its traverse
* callback.
*/
const H5L_class_t UD_soft_class[1] = {{
H5L_LINK_CLASS_T_VERS, /* Version number for this struct.
* This field is always H5L_LINK_CLASS_T_VERS */
(H5L_type_t)UD_SOFT_CLASS, /* Link class id number. This can be any
* value between H5L_TYPE_UD_MIN (64) and
* H5L_TYPE_MAX (255). It should be a
* value that isn't already being used by
* another kind of link. We'll use 65. */
"UD_soft_link", /* Link class name for debugging */
NULL, /* Creation callback */
NULL, /* Move callback */
NULL, /* Copy callback */
UD_soft_traverse, /* The actual traversal function */
NULL, /* Deletion callback */
NULL /* Query callback */
}};
/* First, create a file and an object within the file for the link to
* point to.
*/
file_id = H5Fcreate(SOFT_LINK_FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);
group_id = H5Gcreate2(file_id, TARGET_GROUP, H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
H5Gclose(group_id);
/* This is how we create a normal soft link to the group.
*/
H5Lcreate_soft(TARGET_GROUP, file_id, SOFT_LINK_NAME, H5P_DEFAULT, H5P_DEFAULT);
/* To do the same thing using a user-defined link, we first have to
* register the link class we defined.
*/
H5Lregister(UD_soft_class);
/* Now create a user-defined link. We give it the path to the group
* as its udata.1
*/
H5Lcreate_ud(file_id, UD_SOFT_LINK_NAME, (H5L_type_t)UD_SOFT_CLASS, TARGET_GROUP,
strlen(TARGET_GROUP) + 1, H5P_DEFAULT, H5P_DEFAULT);
/* We can access the group through the UD soft link like we would through
* a normal soft link. This link will still dangle if the object's
* original name is changed or unlinked.
*/
group_id = H5Gopen2(file_id, UD_SOFT_LINK_NAME, H5P_DEFAULT);
/* The group is now open normally. Don't forget to close it! */
H5Gclose(group_id);
H5Fclose(file_id);
}
/* UD_soft_traverse
* The actual traversal function simply needs to open the correct object by
* name and return its ID.
*/
static hid_t
UD_soft_traverse(const char *link_name, hid_t cur_group, const void *udata, size_t udata_size, hid_t lapl_id,
hid_t dxpl_id)
{
const char *target = (const char *)udata;
hid_t ret_value;
/* Pass the udata straight through to HDF5. If it's invalid, let HDF5
* return an error.
*/
ret_value = H5Oopen(cur_group, target, lapl_id);
return ret_value;
}
/* Hard Link example
*
* Create a new class of user-defined links that behave like HDF5's built-in
* hard links.
*
* This isn't very useful by itself (HDF5's hard links already do the same
* thing), but it can serve as an example for how to reference objects by
* address.
*/
/* We need to define the callback functions that the hard link will use.
* These are defined after the example below.
* To keep the example simple, these links don't have a query callback.
* Generally, real link classes should always be query-able.
*/
static herr_t UD_hard_create(const char *link_name, hid_t loc_group, const void *udata, size_t udata_size,
hid_t lcpl_id);
static herr_t UD_hard_delete(const char *link_name, hid_t loc_group, const void *udata, size_t udata_size);
static hid_t UD_hard_traverse(const char *link_name, hid_t cur_group, const void *udata, size_t udata_size,
hid_t lapl_id, hid_t dxpl_id);
static void
hard_link_example(void)
{
hid_t file_id;
hid_t group_id;
H5L_info2_t li;
/* Define the link class that we'll use to register "user-defined hard
* links" using the callbacks we defined above.
* A link class can have NULL for any callback except its traverse
* callback.
*/
const H5L_class_t UD_hard_class[1] = {{
H5L_LINK_CLASS_T_VERS, /* Version number for this struct.
* This field is always H5L_LINK_CLASS_T_VERS */
(H5L_type_t)UD_HARD_CLASS, /* Link class id number. This can be any
* value between H5L_TYPE_UD_MIN (64) and
* H5L_TYPE_MAX (255). It should be a
* value that isn't already being used by
* another kind of link. We'll use 66. */
"UD_hard_link", /* Link class name for debugging */
UD_hard_create, /* Creation callback */
NULL, /* Move callback */
NULL, /* Copy callback */
UD_hard_traverse, /* The actual traversal function */
UD_hard_delete, /* Deletion callback */
NULL /* Query callback */
}};
/* First, create a file and an object within the file for the link to
* point to.
*/
file_id = H5Fcreate(HARD_LINK_FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);
group_id = H5Gcreate2(file_id, TARGET_GROUP, H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
H5Gclose(group_id);
/* This is how we create a normal hard link to the group. This
* creates a second "name" for the group.
*/
H5Lcreate_hard(file_id, TARGET_GROUP, file_id, HARD_LINK_NAME, H5P_DEFAULT, H5P_DEFAULT);
/* To do the same thing using a user-defined link, we first have to
* register the link class we defined.
*/
H5Lregister(UD_hard_class);
/* Since hard links link by object address, we'll need to retrieve
* the target group's address. We do this by calling H5Lget_info
* on a hard link to the object.
*/
H5Lget_info2(file_id, TARGET_GROUP, &li, H5P_DEFAULT);
/* Now create a user-defined link. We give it the group's address
* as its udata.
*/
H5Lcreate_ud(file_id, UD_HARD_LINK_NAME, (H5L_type_t)UD_HARD_CLASS, &(li.u.token), sizeof(H5O_token_t),
H5P_DEFAULT, H5P_DEFAULT);
/* The UD hard link has now incremented the group's reference count
* like a normal hard link would. This means that we can unlink the
* other two links to that group and it won't be deleted until the
* UD hard link is deleted.
*/
H5Ldelete(file_id, TARGET_GROUP, H5P_DEFAULT);
H5Ldelete(file_id, HARD_LINK_NAME, H5P_DEFAULT);
/* The group is still accessible through the UD hard link. If this were
* a soft link instead, the object would have been deleted when the last
* hard link to it was unlinked. */
group_id = H5Gopen2(file_id, UD_HARD_LINK_NAME, H5P_DEFAULT);
/* The group is now open normally. Don't forget to close it! */
H5Gclose(group_id);
/* Removing the user-defined hard link will delete the group. */
H5Ldelete(file_id, UD_HARD_LINK_NAME, H5P_DEFAULT);
H5Fclose(file_id);
}
/* Callbacks for User-defined hard links. */
/* UD_hard_create
* The most important thing this callback does is to increment the reference
* count on the target object. Without this step, the object could be
* deleted while this link still pointed to it, resulting in possible data
* corruption!
* The create callback also checks the arguments used to create this link.
* If this function returns a negative value, the call to H5Lcreate_ud()
* will also return failure and the link will not be created.
*/
static herr_t
UD_hard_create(const char *link_name, hid_t loc_group, const void *udata, size_t udata_size, hid_t lcpl_id)
{
H5O_token_t token;
hid_t target_obj = H5I_INVALID_HID;
herr_t ret_value = 0;
/* Make sure that the address passed in looks valid */
if (udata_size != sizeof(H5O_token_t)) {
ret_value = -1;
goto done;
}
token = *((H5O_token_t *)udata);
//! [H5Oopen_by_token_snip]
/* Open the object this link points to so that we can increment
* its reference count. This also ensures that the token passed
* in points to a real object (although this check is not perfect!) */
target_obj = H5Oopen_by_token(loc_group, token);
//! [H5Oopen_by_token_snip]
if (target_obj < 0) {
ret_value = -1;
goto done;
}
/* Increment the reference count of the target object */
if (H5Oincr_refcount(target_obj) < 0) {
ret_value = -1;
goto done;
}
done:
/* Close the target object if we opened it */
if (target_obj >= 0)
H5Oclose(target_obj);
return ret_value;
}
/* UD_hard_delete
* Since the creation function increments the object's reference count, it's
* important to decrement it again when the link is deleted.
*/
static herr_t
UD_hard_delete(const char *link_name, hid_t loc_group, const void *udata, size_t udata_size)
{
H5O_token_t token;
hid_t target_obj = H5I_INVALID_HID;
herr_t ret_value = 0;
/* Sanity check; we have already verified the udata's size in the creation
* callback.
*/
if (udata_size != sizeof(H5O_token_t)) {
ret_value = -1;
goto done;
}
token = *((H5O_token_t *)udata);
/* Open the object this link points to */
target_obj = H5Oopen_by_token(loc_group, token);
if (target_obj < 0) {
ret_value = -1;
goto done;
}
/* Decrement the reference count of the target object */
if (H5Odecr_refcount(target_obj) < 0) {
ret_value = -1;
goto done;
}
done:
/* Close the target object if we opened it */
if (target_obj >= 0)
H5Oclose(target_obj);
return ret_value;
}
/* UD_hard_traverse
* The actual traversal function simply needs to open the correct object and
* return its ID.
*/
static hid_t
UD_hard_traverse(const char *link_name, hid_t cur_group, const void *udata, size_t udata_size, hid_t lapl_id,
hid_t dxpl_id)
{
H5O_token_t token;
hid_t ret_value = H5I_INVALID_HID;
/* Sanity check; we have already verified the udata's size in the creation
* callback.
*/
if (udata_size != sizeof(H5O_token_t))
return H5I_INVALID_HID;
token = *((H5O_token_t *)udata);
/* Open the object by token. If H5Oopen_by_token fails, ret_value will
* be negative to indicate that the traversal function failed.
*/
ret_value = H5Oopen_by_token(cur_group, token);
return ret_value;
}
/* Plist example
*
* Create a new class of user-defined links that open objects within a file
* based on a value passed in through a link access property list.
*
* Group, dataset, and datatype access property lists all inherit from link
* access property lists, so they can be used instead of LAPLs.
*/
/* We need to define the callback functions that this link type will use.
* These are defined after the example below.
* These links have no udata, so they don't need a query function.
*/
static hid_t UD_plist_traverse(const char *link_name, hid_t cur_group, const void *udata, size_t udata_size,
hid_t lapl_id, hid_t dxpl_id);
static void
plist_link_example(void)
{
hid_t file_id;
hid_t group_id, group2_id;
hid_t gapl_id;
char *path = NULL;
/* Define the link class that we'll use to register "plist
* links" using the callback we defined above.
* A link class can have NULL for any callback except its traverse
* callback.
*/
const H5L_class_t UD_plist_class[1] = {{
H5L_LINK_CLASS_T_VERS, /* Version number for this struct.
* This field is always H5L_LINK_CLASS_T_VERS */
(H5L_type_t)UD_PLIST_CLASS, /* Link class id number. This can be any
* value between H5L_TYPE_UD_MIN (64) and
* H5L_TYPE_MAX (255). It should be a
* value that isn't already being used by
* another kind of link. We'll use 67. */
"UD_plist_link", /* Link class name for debugging */
NULL, /* Creation callback */
NULL, /* Move callback */
NULL, /* Copy callback */
UD_plist_traverse, /* The actual traversal function */
NULL, /* Deletion callback */
NULL /* Query callback */
}};
/* First, create a file and two objects within the file for the link to
* point to.
*/
file_id = H5Fcreate(HARD_LINK_FILE, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);
group_id = H5Gcreate2(file_id, "group_1", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
H5Gclose(group_id);
group_id = H5Gcreate2(file_id, "group_1/group_2", H5P_DEFAULT, H5P_DEFAULT, H5P_DEFAULT);
H5Gclose(group_id);
/* Register "plist links" and create one. It has no udata at all. */
H5Lregister(UD_plist_class);
H5Lcreate_ud(file_id, "plist_link", (H5L_type_t)UD_PLIST_CLASS, NULL, 0, H5P_DEFAULT, H5P_DEFAULT);
/* Create a group access property list to pass in the target for the
* plist link.
*/
gapl_id = H5Pcreate(H5P_GROUP_ACCESS);
/* There is no HDF5 API for setting the property that controls these
* links, so we have to add the property manually
*/
H5Pinsert2(gapl_id, PLIST_LINK_PROP, sizeof(const char *), &(path), NULL, NULL, NULL, NULL, NULL, NULL);
/* Set the property to point to the first group. */
path = "group_1";
H5Pset(gapl_id, PLIST_LINK_PROP, &path);
/* Open the first group through the plist link using the GAPL we just
* created */
group_id = H5Gopen2(file_id, "plist_link", gapl_id);
/* If we change the value set on the property list, it will change where
* the plist link points.
*/
path = "group_1/group_2";
H5Pset(gapl_id, PLIST_LINK_PROP, &path);
group2_id = H5Gopen2(file_id, "plist_link", gapl_id);
/* group_id points to group_1 and group2_id points to group_2, both opened
* through the same link.
* Using more than one of this type of link could quickly become confusing,
* since they will all use the same property list; however, there is
* nothing to prevent the links from changing the property list in their
* traverse callbacks.
*/
/* Clean up */
H5Pclose(gapl_id);
H5Gclose(group_id);
H5Gclose(group2_id);
H5Fclose(file_id);
}
/* Traversal callback for User-defined plist links. */
/* UD_plist_traverse
* Open a path passed in through the property list.
*/
static hid_t
UD_plist_traverse(const char *link_name, hid_t cur_group, const void *udata, size_t udata_size, hid_t lapl_id,
hid_t dxpl_id)
{
char *path;
hid_t ret_value = H5I_INVALID_HID;
/* If the link property isn't set or can't be found, traversal fails. */
if (H5Pexist(lapl_id, PLIST_LINK_PROP) < 0)
goto error;
if (H5Pget(lapl_id, PLIST_LINK_PROP, &path) < 0)
goto error;
/* Open the object by address. If H5Oopen_by_addr fails, ret_value will
* be negative to indicate that the traversal function failed.
*/
ret_value = H5Oopen(cur_group, path, lapl_id);
return ret_value;
error:
return H5I_INVALID_HID;
}
/* Main function
*
* Invokes the example functions.
*/
int
main(void)
{
printf("Testing basic external links.\n");
extlink_example();
printf("Testing external link prefixes.\n");
extlink_prefix_example();
printf("Testing user-defined soft links.\n");
soft_link_example();
printf("Testing user-defined hard links.\n");
hard_link_example();
printf("Testing user-defined property list links.\n");
plist_link_example();
return 0;
}
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